1. Field of the Invention
The present invention is concerned with a high voltage transformer consisting essentially of a magnetic iron core, yokes and primary and secondary coils, with high voltage rectifier and fine control element for the energy supply of single and multi-stage electron accelerators.
2. Discussion of Prior Art
The use of electron streams as energy carriers of high capacity and power density is of ever greater importance in various industrial fields.
The field of electroheat is thereby widened and enriched by new working principles and processes. Besides electron stream welding, melting, annealing and vaporisation, the chemical cross-linking of synthetic resins, as well as the drying and hardening of lacquers by means of accelerated electrons is today an especially cost-favourable and environmentally satisfactory process.
A prerequisite for the industrial use of electron stream technology is the availability of strong and operationally safe electron guns, as well as of the sources of high voltage necessary for the operation thereof and of auxiliary devices therefor.
Since, in the case of lacquer hardening, subsequent cross-linking of lacquers, film cross-linking, laminating or cross-linking of pressure-sensitive adhesives, it is a question of relatively thin layers in the range of from 1 to 300 .mu.m., as electron accelerators there are available so-called one-stage accelerator systems. They can be operated with voltages of up to about 300 keV and, in their construction, are, in comparison with multistage systems, simple and inexpensive. Higher acceleration voltages are of less interest for a wide industrial use in surface and foil technologies for reasons of cost and for reasons of the more expensive shielding against the harder X-rays resulting in the case of braking the electrons.
Electron stream producers of up to 300 keV accelerating voltage can still be screened with lead sheets and thus are not restricted to use in fixedly installed concrete bunkers.
The energy supply for electron accelerators consists of a high voltage device. It provides the acceleration voltage for the electron stream and thus imparts to it its energy. Such a device includes a series of auxiliary devices for measurement, control and regulatory functions, as well as protective and monitoring devices.
Since the present invention is only concerned with the high voltage supply, cathode heating, voltage supply for the control electrodes and for the stream guiding system are not explained in more detail.
As can be seen from the Figure of the accompanying drawing, the high voltage supply comprises the following important features (see, in this regard, also Schroller, Jessat, Vetters, "Hochspannungsanlagen zum Betrieb von Elektronenkanonen, LEW-Nachrichten 1976, Communications from the Forschungsinstitut Manfred von Ardenne, Dresden): fine control element, high voltage transformer and high voltage rectifier.
In the case of high voltage supplies with relatively high acceleration voltages, as fine control elements there are used variable-ratio transformers since they offer the greatest possible safety in the case of surges which occur. Impedances for limiting the short circuit current can also be introduced on the primary side into the current supply. Electronic short circuit suppressors have not proved to be useful in the case of voltages of 300 keV.
The above-described embodiment has the following disadvantages:
The impedances used for limiting the short circuit current must, for reasons of capacity, consist of large-volume coils of low inductivity and, for this reason, offer only insufficient protection for the starting up of an electron accelerator which, after every comparatively great operational interruption, must again be newly activated. Therefore, in the case of the hitherto known devices of the higher voltage class, these impedances must be omitted. Consequently, in the case of spark-overs during the bringing into operation of the stream producer and also during the operation thereof, enormous discharges occur in the stream producer which are further potentiated by the energy subsequently supplied from the primary power supply. Furthermore, in the case of the conventional manner of construction of high voltage transformers, the primary and secondary coils are so constructed that there results a coupling coefficient which is as high as possible in order to be able to operate with as little loss as possible. This construction additionally supports the discharge current in the case of a high voltage spark-over. These discharges can lead to the destruction of the secondary coils or of the rectifier in the high voltage apparatus, in spite of the barrier resistance on the consuming device.